Various vibration generators have been used in conventional vibration testing and other like systems. These vibration generators may be used, for example, in vibration endurance testing conducted to verify that designed and fabricated products (e.g., automobile parts, electronic components, and aircraft parts) can exhibit expected performance in high vibration environments and also in transport and packing testing in which the products are subjected, before being shipped out, to vibration that the products are likely to experience during transport to verify that the products as such can be safely transported.
Many different types of vibration generators have been developed so far: unbalance mass types that produce vibration by a centrifugal force generated by an eccentric mass (weight) coupled to a rotating motor, hydraulic types using a piston, and cam types built around a cam mechanism. There are also electrodynamic vibration generators that utilize an electromagnetic effect (so-called “Fleming's left-hand rule”) that a force acts on a conductor existing in a magnetic field when an electric current flows through the conductor. To briefly explain the operating principles of the electrodynamic vibration generator, a gap is provided in a cylindrical magnetic path, and a drive coil is suspended in the gap by springs so that the coil does not contact the gap. When a DC current flows through an exciting coil in the magnetic path, a magnetic flux is generated, and a DC magnetic field crossing the drive coil at right angles is generated in the gap. A vibration table produces vibration when an AC current flows through the drive coil.
Some fluid-bearing type vibration testers are proposed that include a vibration generator in which a slip table is sustained by externally supplying a pressurized fluid such as oil (see, for example, Patent Document 1). A fluid-bearing type vibration tester supports a slip table without contact, hence exhibits high vibration precision and low frictional wear, and therefore allows extended product life.